A cleaning-crew supervisor tried to frighten his employee, a witness to the Sean Bell shooting, and pressure him to clam up because he didn’t want detectives rooting around his own garbage, court papers show.

“The building is full of blacks that are going to kill you! Don’t testify. You are going to get fired, go to jail and be deported!” Melvin Cordero, 46, admitted he said after he was arrested for interfering in the investigation of the police shooting, authorities said.

“I have a criminal record and I didn’t want the job to find out that I had a criminal record.”

Now Cordero’s record is even longer.

The supervisor was arraigned yesterday on witness-tampering and coercion charges after admitting to authorities he pressured his worker to shut up about the high-profile case.

But the worker, Robert Manaya, decided instead to inform police about his observation. He said he saw a mystery man fire in the direction of the cops, then flee into a nearby building.

Cordero and Manaya work at a cleaning service contracted to maintain the Port Authority’s AirTrain JFK facility in Jamaica.

Manaya was outside dumping trash after 4 a.m. on Nov. 25 when the first of 50 bullets began to fly.

In the months after the shooting, in which cops unloaded on a car full of unarmed men on their way home from a bachelor party, Cordero discouraged Manaya from coming forward.

Manaya talked to the cops anyway, and lied when he told them he didn’t see anything. Then he began thinking about setting the record straight.

Earlier this month, Cordero called the custodian and tried to intimidate him.

“I told him he could be deported and he was going to be arrested and fired,” Cordero said.

But Manaya’s conscience prevailed and on March 14 he strolled into a Jackson Heights station house and, according to sources, told cops his account.

Queens DA Richard Brown interrupted the Bell grand jury’s deliberations so that Manaya could be heard. A day later, two of the five cops involved in the shooting were indicted on first-degree manslaughter charges. A third was indicted for reckless endangerment.

Brown lashed out at Cordero for trying to taint the process.

“One of the major purposes of grand-jury secrecy is to obtain the full cooperation of witnesses and to protect them from outside interference that might affect their testimony,” Brown said.